The braking units for nail drivers of the prior art is to invalidate the trigger of a nail driver when the nail cartridge is empty, so that the user is reminded of reloading the puncher.
The above-mentioned multitude of nails are arranged in a row and inserted in a nail cartridge. They are then pushed to a punch channel one by one by a nail pusher. A user pulls a trigger and a nail in the punch channel is struck by a punch rod so that the nail will embedded in a workpiece. The trigger has a flexible plate and a trigger beam, which trigger beam is controlled by a securing slide rod with a transverse section. One end of the securing slide rod is connected to a fastener guide that situates outside a nail exit and is pressed against the surface of a workpiece when embedding a nail therein. The securing slide rod is used to tilt against the flexible plate so as to pull the trigger.
The punch-restraining technique of the prior art is basically a braking unit mounted on the nail pusher and a securing slide rod, whereby the nail pusher will restrain the securing slide rod when the nails are used up, so that the securing slide rod cannot touch the flexible plate within the trigger. Since the trigger is invalidated, the user will be reminded of reloading the puncher. However, this technique cannot detect whether there is any nail remained in the puncher. Further, it has the disadvantage that the motion of the nail pusher is difficult to control, resulting in the problem of nail jam.
Moreover, the invention disclosed in U.S. Pat. No. 6,267,284 utilizes a latch having a main cam and a second cam, wherein the second cam can restrain a fastener guide when there is any nail in a punch channel, invalidating a punch rod and the punching mechanism. The main cam will be pushed by the nails in the punch channel and rotate the latch to a position where the punch rod can work. However, the invention has the disadvantages as follows.
1. The swing latch does not have a flexible part and a manual control for the swing position of the latch. Without a flexible part, the latch will be short of a precise mechanism for restoring its initial location. When the punch channel is empty and the fastener guide is not engaged with a workpiece, the latch will wiggle, not being able to indicate the status of braking. When the punch channel is empty, it is also impossible to release the punch rod and perform a strike test.
2. The cross section of the main cam is triangular, which requires swing of higher precision in order not to intervene the punch rod in the punch channel. After using for an extended period of time, the main cam is easy to get struck by the punch rod.
3. The swing latch has a nose portion for restraining the fastener guide and an arced second cam. The nose and the second cam are used to restrain the fastener guide, instead of the securing slide rod, which is not consistent with the usual nail drivers having a securing slide rod with a bent transverse section connected to the fastener guide. Therefore, the invention cannot be easily used in common nail driver structures.